Fire extinguishing powders comprising a cellulose ether additive

ABSTRACT

A dry powder fire extinguishant includes a non toxic non hygroscopic fusible additive such that the material acts as an adhesive to retain the powder on a burning surface for a sufficient time for the powder to extinguish the fire. Examples of additives are low melting point resins, low melting point waxes, phosphates of ammonia, potassium or sodium, mercury thiocyanate, microcosmic salt and cellulose ethers of low melting point.

United States Patent Clements 15] 3,673,088 June 27, I972 [54] FIRE EXTINGUISHING POWDERS COMPRISING A CELLULOSE ETHER 21 Appl. No.: 36,674

[30] Foreign Application Priority Data May 14, 1969 Great Britain ..24,479/69 May 14, 1969 Great Britain.... ....24,480/69 Sept. 16, 1969 Great Britain.... ....45,555/69 Sept. 16, 1969 Great Britain ..45,556/69 52 us. Cl ..252/2, 252/3, 252/5, 1 252/7 [51] lnt. Cl. ..A62d 1/00 [58] Field of Search ..252/5, 2, 7, 3; 260/231 R [56] References Cited UNITED STATES PATENTS 1,271,506 7/1918 Ferguson ..252/7 2,232,695 2/ 1941 Durston et a1. ..25 2/5 2,368,209 1/ 1945 Fahey et a1. ..252/2 2,523,377 9/1950 Klug .260/231 R 2,901,427 8/1959 Steppe ..252/5 2,901 ,428 8/ 1959 Schulenburg .....25 2/5 2,937,990 5/1960 Warnock ..252/2 3,055,435 9/ 1962 Warnock et a1. ..252/5 3,407,138 10/1968 Harper et a1 ..252/2 FOREIGN PATENTS 0R APPLICATIONS 716,477 8/1965 Canada ..252/2 Primary Examiner-Robert F. Burnett Assistant Examiner-D. .l. Fritsch AttorneyLarson, Taylor & Hinds 57 ABSTRACT A dry powder fire extinguishant includes a non toxic non hygroscopic fusible additive such that the material acts as an adhesive to retain the powder on a burning surface for a sufficient time for the powder to extinguish the fire.

Examples of additives are low melting point resins, low melting point waxes, phosphates of ammonia, potassium or sodium, mercury thiocyanate, microcosmic salt and cellulose ethers of low melting point.

6 Claims, No Drawings FIRE EXTINGUISHING POWDERS COMPRISING A CELLULOSE ETHER ADDITIVE BACKGROUND OF THE INVENTION This invention relates to dry powder fire extinguishants.

The dry powder fire extinguishant may, for example, be any conventional powder for extinguishing fires such as chalk sodium or potassium carbonate or bicarbonate, borax, magnesium oxide sodium chloride, calcium, lithium or potassium fluorides, potassium or barium chlorides, mica or vermiculite. Another particularly efficacious dry powder fire extinguishant comprises unexpanded or partially expanded perlite.

The dry powder fire extinguishant consists primarily of one of such materials or mixtures thereof, although the powder may contain minor additions of such materials as talc or magnesium carbonate which act as lubricants to improve the flow properties of the powder. Other additives which are used are magnesium stearate and hydrophobic silica which act as water-proofers to inhibit caking of the powder.

Such dry powder fire extinguishants with or without minor lubricant or waterproofing additives are hereinafter referred to as of the kind described. Such dry powder extinguishants can be ineffective when used for extinguishing fires on vertical surfaces. In such cases the powder fails to adhere to the vertical surface and therefore fails to blanket and extinguish the fire.

SUMMARY OF THE INVENTION According to the present invention there is provided a dry powder fire extinguishant of the kind described including a non-hygroscopic non-toxic additive having a low melting point such that the material acts as an adhesive to retain the powder on a burning surface for a sufficient time for the powder to blanket the fire.

The non-hygroscopic non-toxic additive of low melting point may be a material or materials selected from the group consisting of low melting point resins, low melting point waxes phosphates of ammonia, phosphates of potassium, phosphates of sodium, mercury thiocyanate, microcosmic salt and cellulose esters of low melting point.

The additive may be added in amount up to 25 percent by weight of the extinguishant composition although a preferred range is -15 percent by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Particular examples of dry powder fire extinguishants in accordance with the invention is as follows.

Conventional dry powder fire extinguishants such as chalk, sodium or potassium carbonate or bicarbonate, borax, magnesium oxide, sodium chloride, calcium lithium or potassium fluorides, potassium or barium chlorides, mica or vermiculite are ground to have a specific surface area in the range l,000-5,000 cm lgrm. Grinding is for example carried out in a ball mill. The dry powder fire extinguishant may comprise any one of the above materials or mixtures thereof. Shortly before termination of ball milling of the material additives such as l-2 percent by weight hydrophobic silica or 1 percent by weight magnesium stearate which act as waterproofers preventing caking of the powder during storage are added to the material in the ball mill.

Other additives such as l-5 percent by weight of talc or A percent by weight of magnesium carbonate may be included to act as lubricants improving the flow properties of the powder. In accordance with the invention there is then added to the powder in the ball mill an additive comprising a material which is non-hygroscopic non-toxic and having a low melting point. Examples of such materials are:

A low melting point resin such as shellac A low melting point wax such as a high molecular weight parafin Amonium, potassium or sodium phosphate Mercury thiocyanate Microcosmic salt (sodium ammonium hydrogen phosphate) Cellulose ethers of low melting point such as methyl ethyl cellulose and sodium ethyl cellulose The additive may comprise such materials singly or in combination. The material is added to the powder in the ball mill and milling is completed to intimately disperse the material and any other additives in the powder.

The additive may be added in amount up to 25 percent by weight of the extinguishant composition, although a preferred range is 10-15 percent by weight of the extinguishant composition.

It is preferred that the melting point of the additive should be less than the surface temperature of the burning material and not more than 250 C.

Preferably for use the dry powder fire extinguishant is provided in a metal or plastic covered container having means for expelling or dispersing the powder. Argon, carbon dioxide or nitrogen may be used as the driving charge for dispersing the powder. Only the former gas is suitable for reactive metal fires.

A particular form of dry powder extinguishant in accordance with the invention comprises ground unexpanded or partially expanded perlite containing from 5-l5 percent by weight of finely divided methyl-ethyl cellulose or sodium ethyl cellulose, or a combination of these materials. A preferred additive is 10 percent by weight.

Perlite is a naturally occurring siliceous rock of volcanic origin. A typical composition range is:

It is a feature of perlite which distinguishes it from other volcanic glasses that when it is heated it softens over a temperature range 800 1000 C, expanding into a foamy product four to twenty times its original volume. This expansion is caused by combined water which occurs as 4 to 6 percent of crude perlite rock. At a suitable temperature the evenly distributed combined water is vaporized to steam. The result is that on application to a fire ground perlite which is unexpanded or only partially expanded expands and coalesces to create a viscous foam which has considerable thermal resistance as well as the property of excluding the atmosphere where a continuous cover of foam is produced. The addition of methyl-ethyl cellulose or sodium ethyl cellulose to the perlite powder provides for sticking of the perlite powder to a vertical burning surface. The methyl-ethyl cellulose or sodium ethyl cellulose melts on contacting the burning surface and acts in the manner of an adhesive for the perlite powder to retain the powder on the surface for a sufficient time for the perlite powder to expand and blanket the burning surface.

Dispersion of the perlite powder is dependent on the bouyancy of individual particles. The perlite is ball milled to a specific surface area of about 2,000 cm /grrn and a powder size of -300 mesh (8.8.8.) is suitable with this point in mind and because it gives a satisfactory packing density in an extinguisher container when used in the unexpanded form. The perlite may also be partially expanded and good results are obtained with perlite expanded from a density of 70 lbs/cu.ft. to 35 lbs/cu.ft. Fully expanded perlite has a density of about 7 1b/cu.ft.

If desired a further additive such as talc or sodium stearate may be added to improve the fluid properties of the powder extinguisher.

The invention has been found particularly advantageous for dealing with metal fires where the surface temperatures are from about 600 to 1,800" C.

We claim:

1. A dry powder fire extinguishant comprising an additive of a material selected from the group consisting of methyl-ethyl cellulose and sodium ethyl cellulose, said additive acting in the manner of an adhesive to retain the powder extinguishant on a burning surface for a sufficient time for the powder extinguishant to blanket the fire.

2. A dry powder extinguishant as claimed in claim 1 wherein the additive is added in amount up to 25 percent by weight of the extinguishant composition.

3. A dry powder extinguishant as claimed in claim 1 wherein the additive is added in the range 5-15 percent by weight of the extinguishant composition.

4. A dry powder fire extinguishant in which the dry powder comprises ground unexpanded or partially expanded perlite and an additive of a material selected from the group consisting of methyl-ethyl cellulose and sodium ethyl cellulose, said additive acting in the manner of an adhesive to retain the perlite on a burning surface for a sufficient time for the perlite to blanket the fire.

5. A dry powder fire extinguishant as claimed in claim 4 wherein the additive is added in amount up to 25 percent by weight of the extinguishant composition.

6. A dry powder extinguishant as claimed in claim 4 wherein the additive is added in the range 5-15 percent by weight of the extinguishant composition. 

2. A dry powder extinguishant as claimed in claim 1 wherein the additive is added in amount up to 25 percent by weight of the extinguishant composition.
 3. A dry powder extinguishant as claimed in claim 1 wherein the additive is added in the range 5-15 percent by weight of the extinguishant composition.
 4. A dry powder fire extinguishant in which the dry powder comprises ground unexpanded or partially expanded perlite and an additive of a material selected from the group consisting of methyl-ethyl cellulose and sodium ethyl cellulose, said additive acting in the manner of an adhesive to retain the perlite on a burning surface for a sufficient time for the perlite to blanket the fire.
 5. A dry powder fire extinguishant as claimed in claim 4 wherein the additive is added in amount up to 25 percent by weight of the extinguishant composition.
 6. A dry powder extinguishant as claimed in claim 4 wherein the additive is added in the range 5-15 percent by weight of the extinguishant composition. 